Worldwide, about a billion people lack access to safe, clean drinking water. A safe and adequate water supply is essential for the prevention of water borne diseases. Drinking water must be free of organisms and chemical concentrations that are hazardous to human health. It should be free of suspended particles, bad tastes, colors and smells.
Water treatment is the process of making impure water safe to drink and use. Treatment processes are often expensive and require regular attention. Basically, three water conditions need treatment: contaminated water containing disease-causing organisms (pathogens) thereby requiring disinfection; turbid water (water clouded with suspended matter) thereby requiring settling or filtration to obtain clear and clarified water; high mineral or salt containing water which impart the water with bad taste, color or odor thereby requiring conditioning of the water.
Chlorine is the most widely used chemical disinfectant for use in water treatment and is marketed in many forms. The chlorine added to the water reacts with organic and inorganic material as well as disease-causing organisms. The amount of chlorine that is consumed by the treated water is called the “chlorine demand”. The amount of chlorine remaining in the water after the chlorine demand has been satisfied is called “residual chlorine”.
The conventional chlorine-based water treatment compounds include elemental chlorine, sodium hypochlorite and calcium hypochlorite. Elemental chlorine, employed as chlorine gas, is known to be the most cost effective for providing disinfected water. While used extensively in urban treatment systems, it is not commonly available to rural communities because of its handling difficulties (pressurized containers) and safety problems.
Sodium Hypochlorite, or bleach, is more widely available, and can be manufactured locally, but its use is limited primarily because of a short shelf life (3-6 months). Calcium Hypochlorite (CalHypo), despite its lower transport costs, is an expensive and flammable substance that requires special handling and storage.
NaDCC (Sodium dichlor, Sodium dichloro-isocyanurate), a chlorine based chemical disinfectant has recently been approved by the EPA and the WHO for regular human consumption. The material is being used for field applications as a dry solid mainly in a tablet form. Solid NaDCC is highly unstable when moist. The solutions of NaDCC cannot be stored for long periods since their available chlorine content decreases slowly.
Other chlorine based chemicals include trichlorocyanuric acid (TCCA) which may be dosed into water, in the form of a tablet, using feeders (chlorinators) such as the HAYWARD automatic pressure style feeders.
To prepare water treating solutions, the solid chemical disinfectants are preliminarily dissolved in a separate vessel and the resulting mixture constituting the water treating solution is then taken out with suitable dosing pumps and fed into water to be treated. For example, GB 2 403 947 describes a drinking water chlorinating system comprising a container for solid chlorinating substance in tablets with a water nozzle therein connectable to water mains, a settling chamber disposed under the container, a feed chamber in fluid communication with an upper part of the settling chamber, the feed chamber having an outlet connectable to a collection water pipe via a high-pressure pump, the container having water-permeable bottom and being configured so that water emanating from the water nozzle washes the tablets and drips onto the water surface in the settling chamber. The tablets are continuously in a moist state reducing the effectiveness of treatment with NaDCC tablets (for reason such as those discussed above).
Other dosing systems are known. For example, a dissolving tank by Nalco provides a pesticide solution, made by providing water and a chemical agent (Towerbrom 960) directly to the tank during a feed cycle, which may use a dry agent feeding device as disclosed in U.S. Pat. No. 5,427,694.
By way of further example, the Granudos 45/100 system, which is a dosing system for granular calcium hypochlorite (the chemical) used for the disinfection of swimming pools. This device meters the chemical directly from the container (drum). The chemical is dosed into a dissolving system whenever the level of chlorine in the pool falls below a threshold, and the dissolving system is maintained topped up with water continually, either from the pool or from the mains, as required. A solution of the chemical is channeled to the pool, and acid is added in order to prevent precipitation and keep the pool water at the required pH value (7.2-7.6).
US Patent Application Publication No. 2004/0154984 describes a device for dissolution of a particulate material to provide water treating solutions (specifically, biocides) of constant concentrations.
A system for dosing dry flowable material into water is described in U.S. Pat. No. 4,912,68 1. Specifically, a system for creating an admixture from a liquid and a relatively dry flowable material is described, the system includes a hopper for the dry flowable material, a pipe, a pair of valves defining a metering section of the pipe, and a mixing tank into which the dry material and water are introduced. The valves are alternately operated in response to sensed liquid level in the mixing tank to deposit a predetermined quantity of the dry material into the tank, and when the latter occurs, the water is injected tangentially into the tank to create a homogeneous admixture.
U.S. Pat. No. 6,387,251 describes an apparatus for dosing a granulated or powdered material in water to form an admixture, which includes a dosing assembly with a water collecting tank hydraulically connected to inflows of unmixed water and to an outflow of the admixture to water to be treated. Unmixed water is tapped through a duct from an inflow and fed to a substantially tubular manifold, upwardly connected to tank. The material is delivered into the manifold, in which the material mixes with water tapped from the inflow through duct and an admixture discharges into a collecting tank.
WO 2004/041726 discloses a method for treating a body of water with maintenance doses of water treatment chemicals based on the volume of water to be treated.
The following publications are of general background interest, and disclose various types of water treatment devices and systems or related devices/systems: U.S. Pat. No. 6,544,487 B1; WO 03/097537 A1; EP 0 751 097 A2; WO 02/10074 A1; U.S. Pat. No. 6,855,307 B2; WO 2004/052794 A1; U.S. Pat. Nos. 5,427,694; 4,938,385; 4,129,230; 3,595,395; 4,181,702; 4,759,907; 4,732,689; 4,584,106; 4,538,744; 4,293,425.